I will attempt to correct your premise. You can have damage that is not imageable because the damaged cells have been absorbed into the blood stream. Or, the damage is just too small. A focal area of damage will result in a weakness in the function supported by that area. Some functions can 'rewire to other areas. Some are restricted to a specific type of neuron with not enough reserve neurons to rewire through.

It does not take long for the cells to break down and be absorbed if there is circulation to carry away the residue..

The other damage that is not physical would be a build up of toxic waste products. Poor circulation can leave the toxic waste products in place such that there needs to be an improvement in blood chemistry/nutrition to help the toxins clear the brain.

Some literature tends to support that the brain is the last system to clear of toxins since it does not have the same like of lymphatic system as the rest of the body. Either way, if the body is clogged with toxins, the brain is likely clogged.

Stress causes many of these toxins to build up. Lack of proper sleep also causes these toxins to build up. Poor circulation is just as bad.

I hope this is making sense.

btw, The brain does not rewire in a way that is hap hazard. It has coding that prevents this from happening. If an attempt at a connection is wrong, the connection will be rejected. I have actually watched this microscopically in-vivo. (in a test tube or petrie dish with live brain cells) Very interesting. The attempts are hap hazard but the connections are not.

If the rewiring is to a proper type of cells, axons, dendrites, etc. then the connection will become complete and move on to another attempt. The multitude of permutations of these networks is vast so it can take magnitudes of these connections before a fully functioning neural network is established.

When Gabby Gifford goes through her therapy, she is slowly pushing these networks forward. They will not establish unless there is information to pass on. The progression is slow and painstakingly tedious. Sort of like beating a path through the wilderness. One needs to walk that same path over and over before it starts to become recognized as an established path.

Hang in there. Just keep moving forward even when you feel like you are not going anywhere further. As you continue to beat down the path you have already walked, you can start taking steps into uncharted territory.

This is how a baby's brain slowly establishes these same paths.

Remember, it has taken 10 to 20 years and more to just get a mature set of paths throughout the brain. A new path does not get established over-night.